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Subjects

Abstract

Cooling of mechanical resonators is currently a popular topic in many fields of physics including ultra-high precision measurements1, detection of gravitational waves2,3 and the study of the transition between classical and quantum behaviour of a mechanical system4,5,6. Here we report the observation of self-cooling of a micromirror by radiation pressure inside a high-finesse optical cavity. In essence, changes in intensity in a detuned cavity, as caused by the thermal vibration of the mirror, provide the mechanism for entropy flow from the mirror’s oscillatory motion to the low-entropy cavity field2. The crucial coupling between radiation and mechanical motion was made possible by producing free-standing micromirrors of low mass (m ≈ 400 ng), high reflectance (more than 99.6%) and high mechanical quality (Q ≈ 10,000). We observe cooling of the mechanical oscillator by a factor of more than 30; that is, from room temperature to below 10 K. In addition to purely photothermal effects7 we identify radiation pressure as a relevant mechanism responsible for the cooling. In contrast with earlier experiments, our technique does not need any active feedback8,9,10. We expect that improvements of our method will permit cooling ratios beyond 1,000 and will thus possibly enable cooling all the way down to the quantum mechanical ground state of the micromirror.

Acknowledgements

We thank C. Brukner, S. Gröblacher, J. Kofler, T. Jennewein, M. S. Kim, A. Vandaley and D. Vitali for discussion. We acknowledge financial support by the Austrian Science Fund (FWF), by the City of Vienna, by the Austrian NANO Initiative (MNA) and by the Foundational Questions Institute (FQXi).

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Editorial Summary

It's all done with mirrors

Cooling of mechanical resonators is the focus of much research effort because of possible applications in ultra-high precision measurements such as gravitational wave detection. It is also of fundamental interest as using this technique it may be possible to observe a transition between classical and quantum behaviour of a mechanical system. Three groups report advances in this area. Gigan et al. and Arcizet et al. used radiation pressure to freeze out thermal vibrations of tiny mechanical microresonators, or micromirrors. In the right conditions, the mirrors cool from room temperature to about 10 K without outside influence. Once the technique is refined it should be possible to achieve further cooling and to observe the quantum ground state of a micromirror experimentally. In the third paper, Dustin Kleckner and Dirk Bouwmeester use optical feedback to cool a micromirror to sub-kelvin temperatures.